Immediate and late airway response of allergic rhinitis patients to segmental antigen challenge. Characterization of eosinophil and mast cell mediators

Altered adhesion molecule expression and endothelial cell activation accompany the recruitment of human granulocytes to the lung after segmental antigen challenge

Mounting evidence suggests that inflammatory cells recruited to the lung can contribute to the pathogenesis of asthma. The factors governing the activation and recruitment of circulating cells to the lung remain unknown, but an early step in this process is the interaction of adhesion molecules on circulating cells with those on endothelial cells. We used a segmental antigen challenge model followed 18 h later by bronchoalveolar lavage (BAL) to study granulocyte recruitment to the lung in 14 allergic subjects. Using immunofluorescence and flow cytometry, we determined the expression of the adhesion molecules CD11b, L-selectin (LECAM-1), and VLA-4 on BAL and peripheral blood granulocytes. Total cell count and percentages of recovered eosinophils and basophils were significantly increased in BAL fluids from antigen-challenged segments. Compared with their peripheral blood counterparts, CD11b expression was increased 2- to 3-fold on BAL eosinophils, basophils, and neutrophils (n = 9, P less than 0.05). In contrast, L-selectin expression was significantly decreased on BAL cells (n = 3 to 4, P less than 0.05). Similar phenotypic changes were observed on all three cell types, and on neutrophils recovered from saline-challenged control lung segments. In two subjects, VLA-4 alpha (CD49d) expression on BAL eosinophils was 78 +/- 5% of that seen on peripheral blood eosinophils. Because ELAM-1 (endothelial leukocyte adhesion molecule-1, E-selectin) expression occurs during allergic inflammation and is shed after endothelial activation, we used a sensitive enzyme-linked immunosorbent assay to analyze BAL supernatants for a soluble form of this molecule (sELAM-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced superoxide production by alveolar macrophages and air-space cells, airway inflammation, and alveolar macrophage density changes after segmental antigen bronchoprovocation in allergic subjects

Airway inflammation is a principal determinant of airway responsiveness and function in asthma and allergic diseases. Alveolar macrophages (AM) may contribute to inflammation in multiple ways, including release of reactive oxygen species such as superoxide (SO) anion. We hypothesized that SO production by AM increases after segmental bronchoprovocation (SBP) with relevant antigen and contributes to airway injury. Eight ragweed-sensitive subjects with allergic rhinitis were studied by bronchoalveolar lavage and ragweed SBP to determine the SO production and characteristics of cells recruited after antigen challenge. No significant changes in cell numbers or total protein concentration were observed immediately after antigen challenge. Purification (to greater than 94%) of AM on discontinuous gradients of Percoll revealed significantly increased spontaneous and opsonized-zymosan-driven SO production immediately after antigen challenge. Forty-eight hours later, total air-space cells, AM, eosinophils, and total protein concentration were significantly increased in relationship to antigen dose given. Furthermore, both unfractionated air-space cells and purified AM obtained 48 h after antigen challenge released increased amounts of SO anion in response to activator compared with either cells obtained immediately after SBP or those obtained 48 h after saline challenge. In addition, significant increases in high density AM were also seen 48 h after antigen challenge. These data suggest that AM activation occurs immediately after antigen challenge, and that the late airway response to antigen is characterized by the appearance of high density AM, which have potentiated SO release. The increased oxidative burden thereby produced may contribute to increased airway injury.

Platelet-activating factor primes human eosinophil generation of superoxide

Platelet-activating factor (PAF) is a potent inflammatory mediator that can cause airway obstruction and hyperresponsiveness; these processes are also associated with pulmonary eosinophilia, suggesting a link between these two events. Thus, PAF's interaction with eosinophils may provide a mechanism for airway damage. However, direct in vitro activation of eosinophils by PAF requires concentrations that are likely higher than those achieved in vivo. As a result, we investigated whether lower, more physiologic concentrations of PAF could prime eosinophils for subsequent activation to another receptor-stimulated factor, in this case formylmethionylleucylphenylalanine (FMLP). To test this hypothesis, eosinophils were preincubated (1 and 15 min) with low concentrations of PAF (1 x 10(-8) and 1 x 10(-10) M); this exposure to PAF resulted in enhanced generation of superoxide anion to FMLP stimulation. Moreover, similar concentrations of PAF decreased eosinophil density and increased expression of cell surface CR3 receptors. Finally, low, nonactivating concentrations of PAF (1 x 10(-10) to 1 x 10(-8) M) caused transient increases in eosinophil cytosolic free Ca2+ concentrations. Collectively, these responses are consistent with the hypothesis that short-term exposure to low concentrations of PAF primes eosinophils to cause an enhanced inflammatory response upon subsequent activation to another receptor agonist. The consequences of this PAF-associated phenomenon can produce an enhanced inflammatory response and airway injury.